There is generally known a vacuum pump having a casing body secured to a driving machine, a hollow cylinder chamber which is formed in the casing body and has an opening at an end portion of the casing body, a rotor which is rotationally driven in the cylinder chamber, a side plate which blocks the opening of the cylinder chamber, and a pump cover which is disposed at the opposite side of the rotor so as to sandwich the side plate between the pump cover and the rotor and fixed to the casing body. This type of vacuum pump is used to generate vacuum for actuating a power braking device of a vehicle, for example, and it can obtain vacuum by driving a rotor in a cylinder chamber of a casing with a driving machine such as an electric motor or the like (see Patent Document 1, for example).